Disa Orchids

Disa orchids, such as the famous Disa uniflora of South Africa's Table Mountain, are beautiful but have long frustrated the many orchidists who don't know how to grow them successfully, and kill lots of them. I've even heard the genus name jokingly pronounced as "die-sa"! (They are actually named for the heroine of an old Swedish saga.)
Disa uniflora
Image courtesy of Peter Baker
Distributed under the Creative Commons Attribution 2.0 Generic license.
Disas require rather different conditions than many other orchids. But meet their needs and they grow fast! Forget everything you know about growing other orchids if you want to keep these: in particular, they are NOT epiphytes! Also, the conventional wisdom that most orchids die from overwatering does not apply. One could reasonably consider Disas to be water plants, as they are sometimes found completely submerged in nature during certain seasons, and they generally grow right next to streams. You should water them at least daily, set them in buckets of water, or even construct flow tables that keep water flowing past their roots constantly. They should never, ever dry out or they will die.

You need very pure water for these plants: they grow in mountain streams. So unless you want to go to the grocery store to get distilled water every day, invest in a reverse osmosis system. (Your other orchids will appreciate it, too!) Monitor how well your reverse osmosis system is working, changing its membrane as necessary; you want a TDS (Total Dissolved Solids) meter to read less than 200-300 ppm, even after fertilizer is added. They also like an acidic pH; use peat moss or sphagnum moss in the potting mix to achieve this. (They often like to be overpotted in plastic mesh pots, too.)

Since these plants get so much water, you may sometimes need to treat bacterial and fungal diseases. But whatever chemicals you use need to be at low concentrations, because the plants require pure water!

Disas don't like root temperatures above 70°F (21C). Otherwise, they are pretty forgiving about temperatures: they can withstand (very) light frost and temperatures over 100°F (37C), on occasion! Higher humidity should help them withstand high temperatures. Ideally, they should have cool temperatures, below 70°F (21C) by day, and 10-15°F (6-8C) cooler by night. Cool root temperatures are especially important.

They like bright light; direct sunlight is okay, if you can provide it without overheating the roots.

They seem to care a lot about air circulation, so use some fans!

After blooming, the plant will die back, but hopefully you'll already see a number of new shoots growing out of the pot. You should pot these up separately, as the old plant will rot! Also repot them any time they don't appear to be doing well, as it gives you a chance to cut off any rotting roots.

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